Porous ceramics are generally used for fire-resistant insulating materials, water purification materials, humidity conditioning materials, and volatile organic compound (VOC) adsorption materials and the like. The structure of these types of porous ceramics include closed cell-type structures, lattice structures, aggregate-type structures, structures having pores formed from very fine cracks, and structures having continuous interconnected pores, and these may be selected in accordance with the application.
Examples of known lattice structure porous ceramics include structures produced by injecting a ceramic composition into the pores of a foamed urethane resin, subsequently decomposing the resin component, and then performing sintering.
Examples of known aggregate-type porous ceramics include structures in which the spaces between an aggregate of coarse particles in a composition function as pores.
Examples of known closed cell-type porous ceramics include structures in which pores are generated during a firing process by high-temperature decomposition of volatile components within the composition.
Examples of known porous ceramic having pores formed from very fine cracks include structures obtained by sintering a composition obtained by mixing a raw material such as a clay which contracts upon heating and a slag which expands upon heating.
Further, examples of known porous ceramics having continuous interconnected pores include structures obtained by adding an alkaline solution to metallic aluminum within a water-containing composition to generate hydrogen, and then performing sintering.
In recent years, porous ceramics have also started to be used as road surface materials for paved roads, roofing materials and wall materials for buildings, and building materials for greening base materials and the like. Porous ceramics used as building materials must be readily permeable to water (have high water permeability), and also have appropriate water retention properties.
One example of this type of porous ceramic that has been proposed is a porous ceramic sintered body produced by mixing a diatomaceous earth, a clay and an organic sludge, and then sintering the mixture (for example, see Patent Document 1). According to the invention of Patent Document 1, the combination of micrometer order pores which are derived from retained pores of the diatomaceous earth by preventing the clay from entering the pores of the diatomaceous earth, and millimeter order pores which are formed artificially enables both the water permeability and the water retention properties to be enhanced.